Process for production of polymer sheet and optical polymer sheet

ABSTRACT

The present invention provides a process for continuously producing a polymer sheet having an excellent surface smoothness, an apparatus for producing such a polymer sheet, and an optical polymer sheet produced by such a process. The process for producing a polymer sheet comprises coating or laminating, on a polymer base sheet, an ultraviolet-curing resin composition, adhering the coated or laminated polymer base sheet to a member having a smooth surface whose maximum surface roughness (Rmax) satisfies Rmax≦0.1 μm, in a state that the ultraviolet-curing resin composition is soft, and applying an ultraviolet light to transfer smoothness of the smooth surface of the member onto the polymer base sheet.

TECHNICAL FIELD

The present invention relates to a process for efficiently producing apolymer sheet superior in surface smoothness and small in retardation,as well as to an optical polymer sheet produced by the process.

BACKGROUND ART

Glass substrates have been used as a transparent electrode substrate forliquid crystal display device. Liquid crystal display devices using aglass substrate have had problems in that the large thickness of glasssubstrate makes it difficult to produce a liquid crystal display deviceof small thickness and light weight and the use of glass incursinsufficient impact resistance.

To alleviate these drawbacks of liquid crystal display devices using aglass substrate, it has been investigated to use an optical polymersheet for production of a liquid crystal display device of lighterweight and improved impact resistance.

For example, in JP-A-53-68099 and JP-A-54-126559, it is disclosed tocontinuously produce a liquid crystal display device using, in place ofa glass substrate, a long polyester film having a conductive metal oxidevapor-deposited thereon. However, the polyester film (polymer sheet) hasno sufficient surface smoothness, unlike a glass substrate having a verygood surface smoothness as a result of polishing. When, in particular, aSTN (super twisted nematic) type liquid crystal display device isproduced in order to obtain a very fine display, the surface smoothnessof the above polymer sheet becomes a very serious problem because in theliquid crystal display device, display is made utilizing thebirefringence of the liquid crystal present between substrates having asubstrate-to-substrate distance controlled at a 0.1 μm accuracy.

To improve the surface smoothness of polymer sheet, a method wasproposed which comprises casting, on a polished glass or the like, anultraviolet-curing resin composition or a thermosetting resincomposition, both of which are liquid, and curing the composition toobtain a sheet. This method, however, has a problem in that the sheetobtained is fragile and causes cracking or chipping during its handling;therefore, there is no clear advantage by use of the polymer sheet overuse of a glass substrate. Further, the method is low in productivity,resulting in a substrate of high cost.

DISCLOSURE OF THE INVENTION

The present invention aims at providing a process for continuously andefficiently producing a polymer sheet superior in surface smoothness andshowing excellent properties when used as an optical polymer sheet for asubstrate of a liquid crystal display device or the like; and an opticalpolymer sheet superior in the above properties, produced using a resinsuitable for the above process.

The present invention provides the followings.

(1) A process for producing a polymer sheet, which comprises coating orlaminating, on a polymer base sheet, an ultraviolet-curing resincomposition, adhering the coated or laminated polymer base sheet to amember having a smooth surface whose maximum surface roughness (Rmax)satisfies Rmax≦0.1 μm, in a state that the ultraviolet-curing resincomposition is soft, and applying an ultraviolet light to transfersmoothness of the smooth surface of the member onto the polymer basesheet.

(2) A process according to the above (1), wherein the member having asmooth surface can transmit an ultraviolet light of a particularwavelength and, after the ultraviolet light has been applied to theultraviolet-curing resin composition from a side of the member notadhering to the polymer base sheet and the composition has been cured,can be peeled from the polymer base sheet.

(3) A process according to the above (1), wherein the polymer base sheetis transparent and can transmit an ultraviolet light and, after theultraviolet light has been applied to the ultraviolet-curing resincomposition from a side of the polymer base sheet not adhering to themember having a smooth surface and the composition has been cured, canbe peeled from the member.

(4) A process according to any of the above (1) to (3), wherein areleasing agent is continuously fed to the member having a smoothsurface.

(5) A process according to the above (4), which comprises, afterapplication of an ultraviolet light, a step of removing the releasingagent transferred onto the surface of the polymer base sheet.

(6) A process according to the above (4) or (5), wherein the releasingagent contains at least a fluorine compound or a silicon compound.

(7) A process according to any of the above (1) to (6), wherein themember having a smooth surface is a roll.

(8) A process according to any of the above (1) to (6), wherein themember having a smooth surface is an endless belt having a flat area of30 cm or more extending in the movement direction.

(9) A process according to any of the above (1) to (6), wherein themember having a smooth surface is a plastic film having a smoothsurface.

(10) A process according to the above (9), wherein the plastic film issubjected to a slidability-imparting treatment at a side opposite to thesmooth surface.

(11) An apparatus for producing a polymer sheets comprising:

a hollow transparent roll which has a smooth surface whose maximumsurface roughness (Rmax) satisfies Rmax≦0.1 μm and which can transmit anultraviolet light, and

an ultraviolet source placed in the hollow portion of the roll.

(12) An optical polymer sheet produced by a process set forth in any ofthe above (1) to (10).

(13) An optical polymer sheet according to the above (12), wherein thepolymer is a polyethersulfone.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a hollow quartz glass rollhaving a high-pressure mercury lamp inside, which constitutes theproduction apparatus used in Example 1.

FIG. 2 is a schematic view of a transparent endless belt having anultraviolet source inside, which constitutes the production apparatusused in Example 3.

FIG. 3 is a schematic sectional view of the layer constitution obtainedin Example 6.

FIG. 4 is a schematic sectional view of a metal roll of the productionapparatus used in Example 7.

The numerals used in FIGS. 1 to 4 refer to the followings.

1: Rubber-made nip roll

2: Hollow quartz glass roll

3: High-pressure mercury lamp (with a water jacket)

4: Reflector plate

5: Peeling roll

6: Polymer sheet

21: Rubber-made nip roll

22: Mirror-surface roll for driving

23: Transparent endless belt

24: High-pressure mercury lamp

25: Tension roll

26: Peeling roll

27: Polymer sheet

31: Layer subjected to slidability-imparting treatment

32: Plastic film (the side contacting with 33 is a smooth surface)

33: Ultraviolet-cured resin layer

34: Polymer sheet

41: Rubber-made nip roll

42: Metal roll

43: High-pressure mercury lamp (with a water jacket)

44: Reflector plate

45: Releasing agent-feeding roll

46: Peeling roll

47: Polymer sheet

DETAILED DESCRIPTION OF THE INVENTION

As the polymer used in the polymer base sheet of the present invention,there can be mentioned, for example, polyester, polysulfone,polyethersulfone, polyetherketone, polyetheretherketone, polyimide,polyamideimide, polycarbonate, epoxy resin, acrylic resin,norbornene-based polymer and mixed resins thereof. However, the polymeris not restricted thereto. Of these, particularly preferred ispolyethersulfone well balanced in transparency, heat resistance,processability and impact resistance, from the standpoint of productionof a liquid crystal display device. The thickness of the polymer basesheet is preferably 10 μm to 500 μm, more preferably 50 μm to 400 μm.When the thickness of the polymer base sheet is less than 10 μm, thesheet cuts easily, making the handling difficult and, moreover, it isdifficult to maintain the distance between substrates of a liquidcrystal display device. When the thickness is more than 500 μm, thesheet cracks easily when used as a substrate of a liquid crystal displaydevice and bent.

As the ultraviolet-curing resin composition used in the presentinvention, there can be mentioned, for example, a liquidultraviolet-curing resin composition composed mainly of an acrylatecompound or the like, and a sheet-like ultraviolet-curing resincomposition composed mainly of an epoxy resin, an unsaturated polyesterresin or the like. The former resin composition (liquid resincomposition) is coated on a polymer base sheet using a coater and, whenthe composition contains a solvent, the solvent is vaporized using adryer. The latter resin composition (sheet-like resin composition) islaminated on a polymer base sheet. It is possible to use, besides theultraviolet-curing resin, a resin which can be cured by anelectromagnetic wave such as infrared light, visible light, particlebeam, ultrasonic wave or the like, or by an elastic wave.

In the present invention, when the polymer base sheet having aultraviolet-curing resin composition thereon is adhered to a memberhaving a smooth surface of Rmax≦0.1 μm, the ultraviolet-curing resincomposition must be soft or in a liquid state so that smoothness of thesmooth surface of the member can be sufficiently transferred onto theultraviolet-curing resin composition. The ultraviolet-curing resincomposition includes a type which is soft or a liquid per se at roomtemperature even without containing a solvent. When another type isused, it is necessary that heating is conducted by a heater or the likeand then adhesion is made, or that the lamination (adhesion) temperatureis raised and adhesion and softening are made simultaneously.

As the method for adhesion, there are used a nip roll, electric pinning,etc. However, the method is not restricted thereto.

In the present invention, the member having a smooth surface, to beadhered to the polymer base sheet having an ultraviolet-curing resincomposition thereon, must have a surface roughness of Rmax≦0.1 μm. Whenthe Rmax is more than 0.1 μm, it is impossible to obtain a liquidcrystal display device capable of showing good display. As the memberhaving a smooth surface of Rmax≦0.1 μm, there can be mentioned a roll,an endless belt and a plastic film. The roll can be produced bypolishing the surface of a quartz glass tube, a glass tube or achromium-plated roll, and the endless belt can be produced, for example,by polishing the surface of a stainless steel belt or by using a castfilm of a transparent polymer. As the plastic film, there can bementioned, for example, a polyethylene terephthalate (hereinafterreferred to as PET), a film produced by casting, and a surface-polishedfilm. The side of the plastic film opposite to the smooth surface ispreferably subjected to a slidability-imparting treatment, because whenthe plastic film subjected to the treatment is adhered to the polymerbase sheet and transferred through a production line, the transfer speedis increased, the adhesion of foreign matter caused by frictionalelectrification is prevented, and productivity is strikingly increased.Further, when a plastic film is used, it can be peeled after applicationof an ultraviolet light and, therefore, the plastic film can alsofunction as a protective film for prevention of mar formation or foreignmatter adhesion which may occur in a production line. When an endlessbelt is used, it preferably has a flat area of 30 cm or more extendingin the movement direction. By curing the ultraviolet-curing resincomposition on this area, a warpage-free rigid sheet can be obtained.

In the present invention, it is preferred that a releasing treatment isapplied or a releasing agent is continuously fed, to the member having asmooth surface, to be adhered to the polymer base sheet having anultraviolet-curing resin composition thereon. By feeding a releasingagent to the member having a smooth surface, it is possible to preventthe uncured ultraviolet-curing resin from adhering to the member andpeeling from the polymer base sheet. If the feeding of the releasingagent is not continuous, the releasing of the ultraviolet-curing resinis not made satisfactorily. There is no particular restriction as to themethod for continuously feeding the releasing agent; however, there canbe mentioned, for example, a method which comprises continuouslycontacting a member having a smooth rubber surface containing areleasing agent, with the member having a smooth surface to which thepolymer base sheet is to be adhered.

It is preferred that the apparatus for production of a polymer sheetaccording to the present invention has a device for removing thereleasing agent transferred onto the polymer base sheet. Transfer of thereleasing agent onto the polymer base sheet is not desirable because itinvites contamination of the production line. There is no particularrestriction as to the device for removing the releasing agenttransferred onto the polymer base sheet; however, there can bementioned, for example, a cleaning device using an organic solvent.

As to the kind of the releasing agent used in the present invention,there is no particular restriction, either; however, a releasing agentcontaining a fluorine compound (e.g. carbon fluoride) or a siliconcompound (e.g. silicone oil) is preferred.

In the present invention, the curing of the ultraviolet-curing resincomposition can be conducted by using, as the member having a smoothsurface, an ultraviolet-transmittable transparent member having a smoothsurface of Rmax≦0.1 μm and by applying an ultraviolet light (emittedfrom a high-pressure mercury lamp or the like) from behind the memberhaving a smooth surface (that is, from the side of the member oppositeto the smooth surface). Thereby, an ultraviolet-cured resin layer can beformed on the polymer base sheet in a state that the smoothness of thesmooth surface of the member has been transferred onto the resin layer,and a polymer sheet having a smooth surface can be produced. As theultraviolet-transmittable transparent member, there can be mentioned,for example, a quartz roll and a transparent film sheet. For example, ahollow quartz roll having an ultraviolet source in the hollow portion isused and an ultraviolet light is applied from the source via the quartzroll; thereby, an ultraviolet-curing resin can be cured in a state thatthe smoothness of the smooth surface of the member has been transferredonto the resin.

In the present invention, also when there are used, as the member, amember having an opaque smooth surface of Rmax≦0.1 μm and, as thepolymer base sheet, an ultraviolet-transmittable polymer base sheet, andan ultraviolet light is applied from the side of the polymer base sheetopposite to the side having an ultraviolet-curing resin composition, apolymer sheet having a smooth surface can be produced. In this case, thepolymer base sheet used must have transparency; however, since manypolymer sheets have transparency, this method of producing a smoothpolymer sheet is very useful industrially. The polymer sheets producedas above find optical applications and are useful, for example, as atransparent substrate for a liquid crystal display device or as asubstrate for optical mirror.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is hereinafter described by way of Examples.However, the present invention is in no way restricted by the Examples.The optical properties of a sheet were measured according to thefollowing methods.

(1) Thickness of Polymer Sheet

The thicknesses of a polymer sheet were measured in the width directionof the sheet at intervals of 20 mm using a contact type dial gauge, andthe average of the measurements was taken as the thickness of thepolymer sheet.

(2) Maximum Surface Roughness (Rmax) of Polymer Sheet

The surface unevennesses of a polymer sheet were measured in the widthdirection of the sheet over the entire width at scanning intervals of 2mm using a contact type precision level difference meter (ALPHA-STEP 200produced by TENCOR INSTRUMENTS), and the maximum surface unevenness ofthe measurements was taken as the maximum surface roughness (Rmax) ofthe polymer sheet.

(3) Maximum Surface Roughness (Rmax) of Member Having Smooth Surface

The surface unevennesses of a member having a smooth surface weremeasured in the width direction over the entire width at cut-off lengthsof 0.8 mm using a contact type surface roughness tester produced by K.K. Mitsutoyo, and the maximum surface unevenness of the measurements wastaken as the maximum surface roughness (Rmax) of the member having asmooth surface.

EXAMPLE 1

The following operation was made using as a polymer base sheet apolyethersulfone having a thickness of 200 μm and the maximum surfaceroughness (Rmax) of 0.3 μm, and using a sheet-producing apparatuscomprising a payoff, a coater section, a heating and drying zone, ahollow quartz glass roll having a high-pressure mercury lamp in thehollow portion, and a winder. First, as an ultraviolet-curing resincomposition a uniform solution obtained by mixing, at 50° C., 100 partsby weight of an epoxy acrylate prepolymer having a molecular weight of1,540 and a melting point of 70° C. (VR-60, a product of ShowaHighpolymer Co., Ltd.), 300 parts by weight of butyl acetate, 100 partsby weight of cellosolve acetate and 2 parts by weight of benzoin ethylether was coated on the polymer base sheet in a wet film thickness of 5μm, by the gravure roll coater of the coater section; and the coatedpolymer base sheet was heated at 100° C. for 5 minutes in the heatingand drying zone to remove the solvent. The ultraviolet-curing resincomposition after solvent removal was in a paste-like soft state.Successively, the dried sheet was adhered, by using a rubber-made niproll, to the hollow quartz glass roll of diameter=300 mm and Rmax=0.04μm having inside a high-pressure mercury lamp of 80 w/cm (output); anultraviolet light was applied to cure the ultraviolet-curing resincomposition; and the resulting sheet was wound up by the winder tocontinuously obtain a polymer sheet. The exposure time of theultraviolet light was 40 seconds. The Rmax of the obtained polymer sheetat the side which had contacted with the roll, was measured to obtain0.04 μm.

Next, on the polymer sheet was formed a SiO₂ film of 500 Å in thicknessby a DC magnetron method by introducing a mixed gas of oxygen/argon gas(9%) at an initial vacuum of 3×10⁻⁴ Pa and conducting sputtering at avacuum of 3×10⁻¹ Pa. Thereon was formed a transparent conductive filmmade of indium tin oxide (ITO) having an atomic ratio [In/(In+Sn)] of0.98, by a DC magnetron method by introducing a mixed gas ofoxygen/argon gas (4%) at an initial vacuum of 3×10⁻⁴ Pa and conductingsputtering at a vacuum of 1×10⁻¹ Pa. The film thickness was 1,600 Å andthe specific resistance was 4×10⁻⁴ Ω.cm.

Next, on the resulting sheet was coated a resist, and development wasmade. Pattern etching was conducted in an etching solution of 40° C.which was 10 vol. % HCl, whereby a display pattern of diagonal length=3inch and L/S=150 μm/50 μm was formed. Then, an alignment film for STNwas formed by coating and subjected to a firing treatment at 150° C. for2 hours. Thereafter, a rubbing treatment was conducted so as to obtainan alignment of 240° twist. Then, a spacer was spread; a sealing agentwas coated and cured at 130° C. to form a cell; and a liquid crystalcomposition for STN was poured into the cell. A polarizer was attachedat such a location as to give the maximum contrast, whereby a liquidcrystal display device was produced. The liquid crystal display devicewas subjected to an operation test at a driving voltage of 0 to ±5 V; asa result, there was no display unevenness due to the abnormal cell gapof liquid crystal, and good display was obtained.

EXAMPLE 2

The following operation was made using as a polymer base sheet apolycarbonate having the maximum surface roughness (Rmax) of 0.2 μm, andusing a sheet-producing apparatus comprising a payoff, a coater section,a heating and drying zone, a chromium-plated roll of diameter=400 mm andRmax=0.03 μm, a high-pressure mercury lamp of 80 w/cm (output) capableof applying an ultraviolet light to the surface of the chromium-platedroll, and a winder. First, coating to drying of the ultraviolet-curingresin composition were conducted in the same manner as in Example 1.Successively, the resulting sheet was adhered, by using a rubber-madenip roll, to the chromium-plated roll of diameter=400 mm and Rmax=0.03μm controlled at 50° C.; an ultraviolet light was applied from the sideof the polymer base sheet opposite to the ultraviolet-curing resincomposition side, using the high-pressure mercury lamp of 80 w/cm(output), to cure the ultraviolet-curing resin composition; theresulting sheet was wound up by the winder to continuously obtain apolymer sheet. The exposure time of the ultraviolet light was 30seconds. The Rmax of the obtained polymer sheet at the side which hadcontacted with the roll, was measured to obtain 0.03 μm.

A liquid crystal display device was produced in the same manner as inExample 1. The liquid crystal display device was subjected to anoperation test at a driving voltage of 0 to ±5 V; as a result, there wasno display unevenness due to the abnormal cell gap of liquid crystal,and good display was obtained.

EXAMPLE 3

The following operation was made using as a polymer base sheet apolyethersulfone having a thickness of 200 μm and the maximum surfaceroughness (Rmax) of 0.3 μm, and using a sheet-producing apparatuscomprising a payoff, a coater section, a heating and drying zone, a niproll, a norbornene-based polycycloolefin-made endless belt of Rmax=0.04μm having inside a high-pressure mercury lamp, and a winder. First, asan ultraviolet-curing resin composition a uniform solution obtained bymixing, at 50° C., 100 parts by weight of an epoxy acrylate prepolymerhaving a molecular weight of 1,540 and a melting point of 70° C. (VR-60,a product of Showa Highpolymer Co., Ltd.), 200 parts by weight of butylacetate, 100 parts by weight of cellosolve acetate and 2 parts by weightof benzoin ethyl ether was coated on the polymer base sheet in a wetfilm thickness of 10 μm, by the kiss-roll coater of the coater section;and the coated polymer base sheet was heated at 100° C. for 5 minutes inthe heating and drying zone to remove the solvent. Theultraviolet-curing resin composition after solvent removal was in apaste-like soft state. Successively, the ultraviolet-curing resincomposition side of the dried sheet was adhered, by using a rubber-madenip roll, to the norbornene-based polycycloolefin-made endless belt ofRmax=0.04 μm having a flat area of 50 cm extending in the movementdirection and having inside a high-pressure mercury lamp of 100 w/cm(output) (the belt being driven by mirror-surface rolls of Rmax=0.02μm); an ultraviolet light was applied to cure the ultraviolet-curingresin composition; and the resulting sheet was peeled from the endlessbelt and wound up by the winder to continuously obtain a polymer sheet.The exposure time of the ultraviolet light was 40 seconds. The Rmax ofthe obtained polymer sheet at the side which had contacted with thebelt, was measured to obtain 0.04 μm.

Next, on the polymer sheet was formed a SiO₂ film of 500 Å in thicknessby a DC magnetron method by introducing a mixed gas of oxygen/argon gas(9%) at an initial vacuum of 3×10⁻⁴ Pa and conducting sputtering at avacuum of 3×10⁻¹ Pa. Thereon was formed a transparent conductive filmmade of indium tin oxide (ITO) having an atomic ratio [In/(In+Sn)] of0.98, by a DC magnetron method by introducing a mixed gas ofoxygen/argon gas (4%) at an initial vacuum of 3×10⁻⁴ Pa and conductingsputtering at a vacuum of 1×10⁻¹ Pa. The film thickness was 1,600 Å andthe specific resistance was 4×10⁻⁴ Ω.cm.

Next, on the resulting sheet was coated a resist, and development wasmade. Pattern etching was conducted in an etching solution of 40° C.which was 10 vol. % HCl, whereby a display pattern of diagonal length=3inch and L/S=150 μm/50 μm was formed. Then, an alignment film for STNwas formed by coating and subjected to a firing treatment at 150° C. for2 hours. Thereafter, a rubbing treatment was conducted so as to obtainan alignment of 240° twist. Then, a spacer was spread; a sealing agentwas coated and cured at 130° C. to form a cell; and a liquid crystalcomposition for STN was poured into the cell. A polarizer was attachedat such a location as to give the maximum contrast, whereby a liquidcrystal display device was produced. The liquid crystal display devicewas subjected to an operation test at a driving voltage of 0 to ±5 V; asa result, there was no display unevenness due to the abnormal cell gapof liquid crystal, and good display was obtained.

EXAMPLE 4

The following operation was made using as a polymer base sheet apolycarbonate having the maximum surface roughness (Rmax) of 0.2 μm, andusing a sheet-producing apparatus comprising a payoff, a coater section,a heating and drying zone, a stainless steel-made endless belt of Rmax0.03 μm having a flat area of 60 cm extending in the movement directionof the belt, a high-pressure mercury lamp of 80 w/cm (output) capable ofapplying an ultraviolet light to the surface of the endless belt, and awinder. First, coating to drying of the ultraviolet-curing resincomposition were conducted in the same manner as in Example 3.Successively, the ultraviolet-curing resin composition side of theresulting sheet was adhered to the surface of the endless belt by usinga rubber-made nip roll; an ultraviolet light was applied from the sideof the polymer base sheet opposite to the ultraviolet-curing resincomposition side, using the high-pressure mercury lamp of 80 w/cm(output), to cure the ultraviolet-curing resin composition; theresulting sheet was wound up by the winder to continuously obtain apolymer sheet. The exposure time of the ultraviolet light was 30seconds. The Rmax of the obtained polymer sheet at the side which hadcontacted with the belt, was measured to obtain 0.03 μm.

A liquid crystal display device was produced in the same manner as inExample 3. The liquid crystal display device was subjected to anoperation test at a driving voltage of 0 to ±5 V; as a result, there wasno display unevenness due to the abnormal cell gap of liquid crystal,and good display was obtained.

EXAMPLE 5

The following operation was made using as a polymer base sheet apolyethersulfone having a thickness of 200 μm and the maximum surfaceroughness (Rmax) of 0.3 μm, and using a sheet-producing apparatuscomprising a payoff, a coater section, a heating and drying zone, aplastic film, a high-pressure mercury lamp and a winder. First, as anultraviolet-curing resin composition a uniform solution obtained bymixing, at 50° C., 100 parts by weight of an epoxy acrylate prepolymerhaving a molecular weight of 1,540 and a melting point of 70° C. (VR-60,a product of Showa Highpolymer Co., Ltd.), 300 parts by weight of butylacetate, 100 parts by weight of cellosolve acetate and 2 parts by weightof benzoin ethyl ether was coated on the polymer base sheet in a wetfilm thickness of 5 μm, by the gravure roll coater of the coatersection; and the coated polymer base sheet was heated at 100° C. for 5minutes in the heating and drying zone to remove the solvent. Theultraviolet-curing resin composition after solvent removal was in apaste-like soft state. Successively, the dried sheet was adhered, byusing a nip roll, to PET (as a plastic film) of Rmax=0.06 μm; anultraviolet light of 80 w/cm was applied to cure the ultraviolet-curingresin composition; and the resulting sheet was wound up by the winder tocontinuously obtain a polymer sheet. The exposure time of theultraviolet light was 10 seconds. The Rmax of the obtained polymer sheetat the side which had contacted with the plastic film, was measured toobtain 0.06 μm.

Next, on the polymer sheet peeled from the plastic film was formed aSiO₂ film of 500 Å in thickness by a DC magnetron method by introducinga mixed gas of oxygen/argon gas (9%) at an initial vacuum of 3×10⁻⁴ Paand conducting sputtering at a vacuum of 3×10⁻¹ Pa. Thereon was formed atransparent conductive film made of indium tin oxide (ITO) having anatomic ratio [In/(In+Sn)] of 0.09, by a DC magnetron method byintroducing a mixed gas of oxygen/argon gas (4%) at an initial vacuum of3×10⁻⁴ Pa and conducting sputtering at a vacuum of 1×10⁻¹ Pa. The filmthickness was 1,600 Å and the specific resistance was 4×10⁻⁴ Ω.cm.

Next, on the resulting sheet was coated a resist, and development wasmade. Pattern etching was conducted in an etching solution of 40° C.which was 10 vol. % HCl, whereby a display pattern of diagonal length=3inch and L/S=150 μm/50 μm was formed. Then, an alignment film for STNwas formed by coating and subjected to a firing treatment at 150° C. for2 hours. Thereafter, a rubbing treatment was conducted so as to obtainan alignment of 240° twist. Then, a spacer was spread; a sealing agentwas coated and cured at 130° C. to form a cell; and a liquid crystalcomposition for STN was poured into the cell. A polarizer was attachedat such a location as to give the maximum contrast, whereby a liquidcrystal display device was produced. The liquid crystal display devicewas subjected to an operation test at a driving voltage of 0 to ±5 V; asa result, there was no display unevenness due to the abnormal cell gapof liquid crystal, and good display was obtained.

EXAMPLE 6

The following operation was made using as a polymer base sheet apolycarbonate having the maximum surface roughness (Rmax) of 0.2 μm, andusing a sheet-producing apparatus comprising a payoff, a coater section,a heating and drying zone, a PET as a plastic film whose one side had aRmax of 0.06 μm and whose other side had been subjected to aslidability-imparting treatment, a high-pressure mercury lamp and awinder. First, coating to drying of the ultraviolet-curing resincomposition were conducted in the same manner as in Example 5.Successively, the resulting sheet was adhered, by using a nip roll, tothe Rmax=0.06 μm side of the PET controlled at 80° C.; an ultravioletlight was applied from the side of the polymer base sheet opposite tothe ultraviolet-curing resin composition side, using the high-pressuremercury lamp of 80 w/cm (output), to cure the ultraviolet-curing resincomposition; the resulting sheet was wound up by the winder tocontinuously obtain a polymer sheet having a constitution as shown bythe schematic sectional view of FIG. 3. The exposure time of theultraviolet light was 30 seconds. The Rmax of the obtained polymer sheetat the side which had contacted with the plastic film, was measured toobtain 0.06 μm. The number of the foreign matter which adhered to thepolymer sheet owing to frictional charging, was small.

A liquid crystal display device was produced in the same manner as inExample 5. The liquid crystal display device was subjected to anoperation test at a driving voltage of 0 to ±5 V; as a result, there wasno display unevenness due to the abnormal cell gap of liquid crystal,and good display was obtained.

EXAMPLE 7

The following operation was made using as a polymer base sheet apolyethersulfone having a thickness of 200 μm and the maximum surfaceroughness (Rmax) of 0.3 μm, and using a sheet-producing apparatuscomprising a payoff, a coater section, a heating and drying zone, ametal roll, a releasing agent-feeding roll, a high-pressure mercury lampand a winder. First, as an ultraviolet-curing resin composition auniform solution obtained by mixing, at 50° C., 100 parts by weight ofan epoxy acrylate prepolymer having a molecular weight of 1,540 and amelting point of 70° C. (VR-60, a product of Showa Highpolymer Co.,Ltd.), 300 parts by weight of butyl acetate, 100 parts by weight ofcellosolve acetate and 2 parts by weight of benzoin ethyl ether wascoated on the polymer base sheet in a wet film thickness of 5 μm, by thegravure roll coater of the coater section; and the coated polymer basesheet was heated at 100° C. for 5 minutes in the heating and drying zoneto remove the solvent. The ultraviolet-curing resin composition aftersolvent removal was in a paste-like soft state. Successively, the driedsheet was adhered, by using a nip roll, to the metal roll ofdiameter=400 mm and Rmax=0.04 μm, and an ultraviolet light of 80 w/cmwas applied from the side of the base sheet opposite to theultraviolet-curing resin composition side to cure the ultraviolet-curingresin composition. The metal roll was contacted with a silicone rubberroll capable of feeding a silicone oil-containing releasing agent, andthe releasing agent was continuously fed onto the surface of the metalroll. The resulting sheet was wound up by the winder to continuouslyobtain a polymer sheet. The exposure time of the ultraviolet light was40 seconds. The Rmax of the obtained sheet at the side which hadcontacted with the metal roll, was measured to obtain 0.04 μm.

Next, on the polymer sheet was formed a SiO₂ film of 500 Å in thicknessby a DC magnetron method by introducing a mixed gas of oxygen/argon gas(9%) at an initial vacuum of 3×10⁻⁴ Pa and conducting sputtering at avacuum of 3×10⁻¹ Pa. Thereon was formed a transparent conductive filmmade of indium tin oxide (ITO) having an atomic ratio [In/(In+Sn)] of0.98, by a DC magnetron method by introducing a mixed gas ofoxygen/argon gas (4%) at an initial vacuum of 3×10⁻⁴ Pa and conductingsputtering at a vacuum of 1×10⁻¹ Pa. The film thickness was 1,600 Å andthe specific resistance was 4×10⁻⁴ Ω.cm.

Next, on the resulting sheet was coated a resist, and development wasmade. Pattern etching was conducted in an etching solution of 40° C.which was 10 vol. % HCl, whereby a display pattern of diagonal length=3inch and L/S=150 μm/50 μm was formed. Then, an alignment film for STNwas formed by coating and subjected to a firing treatment at 150° C. for2 hours. Thereafter, a rubbing treatment was conducted so as to obtainan alignment of 240° twist. Then, a spacer was spread; a sealing agentwas coated and cured at 130° C. to form a cell; and a liquid crystalcomposition for STN was poured into the cell. A polarizer was attachedat such a location as to give the maximum contrast, whereby a liquidcrystal display device was produced. The liquid crystal display devicewas subjected to an operation test at a driving voltage of 0 to ±5 V; asa result, there was no display unevenness due to the abnormal cell gapof liquid crystal, and good display was obtained.

Comparative Example 1

A polymer sheet was continuously obtained by making the same operationas in Example 5 except that the sheet-producing apparatus comprising apayoff, a coater section, a heating and drying zone, a laminate roll, ahigh-pressure mercury lamp and a winder was replaced by an apparatuscomprising a payoff, a coater section, a heating and drying zone, ahigh-pressure mercury lamp and a winder and no member having a smoothsurface was used and an ultraviolet light was applied for 40 secondsfrom the side of the polymer base sheet coated with theultraviolet-curing resin composition, using the high-pressure mercurylamp of 80 w/cm (output). The Rmax of the polymer sheet at theultraviolet-curing resin composition side was measured to obtain 0.2 μm.Thereafter, a liquid crystal display device was produced in the samemanner as in Example 5. The device was subjected to an operation test ata driving voltage of 0 to ±5 V; as a result, display unevenness owing tothe abnormal cell gap of liquid crystal was seen at the positionscorresponding to the Rmax points of the polymer sheet.

All the liquid crystal display devices produced using each of thepolymer sheets of Examples 1 to 7 showed good display. That is, anoptical polymer sheet of good surface smoothness could be obtained ineach of Examples 1 to 7. In contrast, no polymer sheet of good surfacesmoothness could be obtained in Comparative Example 1 because theapplication of ultraviolet light and the curing of ultraviolet-curingresin composition was made using no member of Rmax≦0.1 μm; as a result,the resultant liquid crystal display device showed display unevenness.

Thus, by using the process of the present invention, polymer sheets ofgood surface smoothness could be produced stably, efficiently andcontinuously. The sheets produced by the present process were verysuitable as an optical polymer sheet and, when used as a transparentelectrode substrate in a liquid crystal display device, were light andresistant to cracking as compared with glass substrates and gave nodisplay unevenness, i.e. good display.

Industrial Applicability

According to the present invention, an optical polymer sheet superior insurface smoothness and small in retardation can be produced efficientlyand continuously. Therefore, the sheet can be applied to a light andimpact-resistant display substrate used in liquid crystal displaydevice, electroluminescence device or the like and may also be appliedto optical materials for optical disc, waveguide, etc.

What is claimed is:
 1. A process for producing a polymer sheet, whichcomprises coating or laminating, on a polymer base sheet, anultraviolet-curing resin composition, and then drying the coated polymerbase sheet; adhering the coated or laminated polymer base sheet to amember having a smooth surface whose maximum surface roughness, Rmax,satisfies Rmax≦0.1 μm, in a state that the ultraviolet-curing resincomposition is soft even after drying; and applying an ultraviolet lightto transfer smoothness of the smooth surface of the member onto theultraviolet curing resin composition on the polymer base sheet.
 2. Aprocess according to claim 1, further comprising wherein the memberhaving a smooth surface can transmit an ultraviolet light of aparticular wavelength and, after the ultraviolet light has been appliedto the ultraviolet-curing resin composition from a side of the membernot adhering to the polymer base sheet and the composition has beencured, peeling said member from the polymer base sheet.
 3. A processaccording to claim 1, further comprising wherein the polymer base sheetis transparent and can transmit an ultraviolet light and, after theultraviolet light has been applied to the ultraviolet-curing resincomposition from a side of the polymer base sheet not adhering to themember having a smooth surface and the composition has been cured,peeling said polymer base sheet from the member.
 4. A process accordingto claim 1, wherein a releasing agent is continuously fed to the memberhaving a smooth surface.
 5. A process according to claim 4, whichcomprises, after application of an ultraviolet light, a step of removingthe releasing agent transferred onto the surface of the polymer basesheet.
 6. A process according to claim 4, wherein the releasing agentcontains at least a fluorine compound or a silicon compound.
 7. Aprocess according to claim 1, wherein the member having a smooth surfaceis a roll.
 8. A process according to claim 1, wherein the member havinga smooth surface is an endless belt having a flat area of 30 cm or moreextending in the movement direction.
 9. A process according to claim 1,wherein the member having a smooth surface is a plastic film having asmooth surface.
 10. A process according to claim 9, wherein the plasticfilm is subjected to a slidability-imparting treatment at a sideopposite to the smooth surface.
 11. The process according to claim 2further comprising forming an SiO₂ film on said polymer sheet bysputtering a conductive film thereon.
 12. The process according to claim11 further comprising coating said polymer sheet having a conductivefilm thereon with a resist and developing a pattern with an etchingsolution.